This invention relates to a device for measuring the length of a weft for shuttleless looms, such as a jet loom.
Generally, in a jet loom, a predetermined length of weft required for one weft inserting operation is preliminarily transferred with an air flow toward a storge pipe, and stored therein and the stored weft is caused by the air flow to be transferred through a warp shed upon weft insertion. Such a weft length measuring device, of the so-colled pipe type causes the stored weft to be subject to a relatively strong resistance when it is drawn out of the pipe by the air flow upon the weft insertion. Furthermore, since the transfer of the weft into the storage pipe relies on the air flow, it is difficult to store the exact length of a weft in the pipe. This results in disadvantages, such as an unreliable weft inserting operation leading to a weft insertion error.
In order to remove the disadvantages of said so-called pipe type measuring device, heretofore, a drum type measuring device has been provided as disclosed, for example, in Japanese patent specification No. 46-4872, which device comprises a weft storage drum mounted against rotation, and a weft guide mounted for rotation around the drum to cause the weft supplied from a weft supply bobbin to be wound continuously on the drum periphery in the form of a coil and the wound weft to be unwound upon the weft insertion. However, said device in Japanese patent specification No. 46-4872 is for a gripper loom and is not required to exactly measure the length of a weft necessary for one weft insertion. Therefore, even if said device were intended for use in an air jet loom, it would not be utilized in practice because of relatively great variations in the length of a weft unwound from the weft storage drum during every weft inserting operation.
Furthermore, in said drum type device, when the weft is unwound from the storage drum at the weft insertion, the weft is subject to a smaller resistance than in the so-called pipe device. Also, the drum type device contributes to a stable weft inserting operation. However, the resistance, which the weft is subject to in the drum type device, is not small enough, since the outer peripheral surface of the weft storage drum is made simply in a substantially cylindrical form, which causes the whole weft on the drum to be in sliding contact with the outer peripheral surface of said storage drum when it is unwound therefrom.
It is further stated that the storage drum is of one-piece integral formation so that its diameter remains unchanged. This allows a constant amount of weft to be wound on the storage drum by the weft guide, but involves the disadvantage that the storage drum cannot accommodate itself to a change in the length of weft necessary for one weft insertion, which change may be caused for some reason such as an error in the manufacturing and assembling of the loom.
In order to remove the above disadvantages of said drum type device, Japanese patent specification No. 50-31229 has disclosed an arrangement comprising a plurality of endless belts each consisting of a timing belt arranged in parallel with and equidistant from the other timing belts in the direction of weft insertion, and a plurality of length determining pins provided in each of the endless belts so as to project therefrom. The length of weft necessary for each weft insertion is successively wound between the preceding and succeeding length measuring pins and, at the same time, the weft wound between other preceding and succeeding pins is released to be inserted through the warp shed.
However, it will be understood that the above-discussed device of said Japanese patent specification includes, in addition to said plural end belts and length measuring pins, a complex driving means comprising driving and driven rollers and so on. This makes the arrangement difficult to manufacture, assemble, inspect and repair.
It is therefore a primary object of this invention to provide a weft length measuring device which allows a reliable, stable and speedy weft inserting operation and has a simple structure making said measuring device easy to manufacture, assemble, inspect and repair.
It is another object of this invention to provide a weft length measuring device which provides a reduced area of contact between a weft storage drum and a weft, thereby to decrease the frictional resistance therebetween.
A further object of this invention is to provide a weft length measuring device the weft storage drum of which can be changed in diameter so that the length of weft to be wound thereon is adjustable.